Chapter 17 (spectroscephy) Flashcards
1
Q
What is mass spectrometry used for ?
A
- identify molecular mass of an unknown or known compound
2
Q
What is the molecular ion ?
A
molecular ion (m+): the organic compound that is put into the mass spec, loses an electron and forms a positive ion
3
Q
What is fragmentation ?
A
- The molecular ion breaks down into smaller pieces (fragments)
- other peaks in mass spec are caused by fragment ions formed from the breakdown of the molecular ion
- fragment ions are always positively charged
- when molecular ions fragment non charged radicals form which are not detected by the mass spec
4
Q
How does mass spectrometry work ?
A
- 4 steps: ionisation, acceleration, deflation, detection
- molecule is ionised and fragmented
- the base peak is the most abundant peak
5
Q
How do you used fragments to identify a compound ?
A
E.g ethanol:
- M + at m/z = 46
- small m + 1 peak at m/z = 47
- link fragments to orignal molecule
6
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7
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8
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9
Q
How does infrared spectroscopy work ?
A
- IR causes covalent bonds to vibrate more and absorb energy
- molecules will absorb IR energy at a frequency corresponding to the frequency of the bond natural vibration
- IR spec detects how the absorption of a sample of a sample varies with wave number
- it used to identify functional groups that are present in a molecule
10
Q
What happens to atmospheric gasses because of IR ?
A
- absorption of IR radiation by atmospheric gasses containing C-O, O-H, C-H
- vibrating bonds in the bonds re-emit the absorbed energy from the sun as radiation that increases the temperature of the atmosphere, this leads to global warming
11
Q
What factors affect vibration of bonds ?
A
- the strength of the covalent bond
- mass of the atoms in the bonds, heavier atoms vibrate at a lower frequency, e.g C-Br absorbs a lower frequency than C-Cl
12
Q
What are the uses of IR ?
A
- measure carbon monoxide, carbon dioxide and hydrocarbons
- breathalysers, determine levels of alcohol
13
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